The administration of oxygen to a patient usually has an adverse drying effect on the patient's respiratory system Therefore, various humidifying or nebulizing devices have been used to condition oxygen being administered to a patient by mixing it with water or aqueous solutions.
A typical nebulizer system for inhalation therapy comprises a bottle or like container of sterile liquid, such as water, and a nebulizer assembly. The nebulizer assembly is usually connected to a supply of pressurized oxygen through appropriate throttling valves. As the oxygen flows through an orifice or a venturi device in the nebulizer it creates a negative pressure which draws liquid from the container tube to the nebulizer assembly through a suction and generates an aerosol spray.
The nebulizer assembly admixes the oxygen with the water to produce a humidified oxygen stream which is delivered to a patient through an outlet. The outlet is connected to a delivery hose extending to the patient to be supplied. However, only a small portion of the water drawn to the nebulizer assembly humidifies the oxygen. The majority of the water is returned to the same container from which it was drawn. Most nebulizer systems also use ambient air to dilute the oxygen in the gas stream.
In inhalation therapy, the humidified oxygen flow usually is warmed before it is administered to the patient. U.S. Pat. No. 4,267,974 to Kienholz et al. and my U.S. Pat. No. 4,427,004 to Miller are but two examples of nebulizer systems which warm a humidified oxygen flow before it is administered to a patient.
The Kienholz et al. nebulizer device includes a nebulizer chamber having a throat from which an aerosol spray pattern is emitted in a generally downward path or direction. The Kienholz et al. device also includes a plastic body formed with a well wherein a heater element is provided for heating the water collected in the well which, in turn, introduces water vapor in the gas stream to a patient. The well and heater element are positioned at a location laterally offset from an outlet end of the throat from which the aerosol spray is emitted.
During operation, the heater element of the Keinholz et al. device is immersed in water collected in the well. When the well is filled, overflow is directed back into a water supply bottle through a return tube. The return of water from the well to the supply bottle results in a rising water temperature in the supply bottle which subsequently causes a rising aerosol spray temperature. As will be readily recognized, this condition may result in spray temperature control problems inasmuch as the amount of heat input to the gas stream and the liquid supply is not readily controllable.
My U.S. Pat. No. 4,427,004 discloses a nebulizer device having a tubular core open at its lower end to a water supply bottle. The tubular core is heated to a desired temperature by an electronically controlled heat source. Small liquid droplets emitted from a nebulizer chamber located at a top end of the core impinge against sides of the tubular core and the resulting downwardly flowing sheath of water is vaporized, wholly or in part, to provide heat input to the inhalation gas mixture. The warmed aerosol spray not used as part of the inhalation mixture is immediately returned to the water supply bottle. The return of heated water to the supply bottle makes it difficult to control spray temperature and, thus, the temperature of the humidified gas mixture to the patient.
Moreover, heaters that warm the liquid supply along its path to the aerosol-generating station usually lack sufficient heating capacity to raise the liquid temperature adequately when room air is entrained to dilute the oxygen stream.
In a humidifier system, a heater vaporizes a small reservoir of liquid by boiling within the system. A drawback of these particular heaters is that if the oxygen flow to the humidifier is inadvertently interrupted, the heater may provide too much heat to the reservoir thus overheating the gas stream to be inhaled or otherwise creating a hazardous condition.
As mentioned hereinabove, most nebulizer systems use ambient air to dilute the oxygen content of the gas stream inhaled by the patient. When air is entrained to dilute the oxygen content, total gas flow to the patient is a function of the amount of air entrained. While less heat input will be required to warm the humidified spray at zero entrainment (pure oxygen) as at full entrainment, the heater of the nebulizer system, however, may not always be properly adjusted by the practitioner in the field when the entrainment is modulated. This can result in undesirably high aerosol temperatures.
Neither the Kienholz et al. nor the Miller device provide a self-regulating system which automatically compensates for modulation of ambient air entrainment.
While various advances in the art of inhalation therapy have been made, problems with currently known nebulizer devices remain. In addition to those problems addressed above, known nebulizer systems are typically too expensive to be disposable or are difficult to resterilize and clean after use. Existing nebulizers are also limited in the moisture input they can provide to the oxygen-enriched breathing gas. Moreover, known nebulizing systems have problems in maintaining a particular temperature for the humidified oxygen stream when it is administered to a patient.
Also, commercially available nebulizers are relatively noisy and use more oxygen than is necessary to provide an aerosol inhalation spray. Due to the lack of accuracy of prior art devices and the many variables involved in the inhalation therapy environment, no prior art device to date has proven capable of providing an adequate output of humidified breathable gas having a controlled temperature when administered to he patient.